Cancer Is Not the Answer—Getting Upset by PET False Positives in the Head, Neck, and Skull Base

Positron emission tomography (PET) and computed tomography (CT) is a dual-modality radiographic technique that typically utilizes the radiopharmaceutical F-18 flourodeoxyglucose (FDG), although additional tracers such as Ga-68 DOTATATE may be utilized for neuroendocrine tumors. Because tumor cells rapidly proliferate and have a need for increased glucose utilization from upregulated hexokinase activity, the FDG radiopharmaceutical glucose analog is taken up by tumor cells, with a rate of uptake in proportion to the tumor activity. FDG is phosphorylated to FDG-6-phosphate, within metabolically active tumor cells and releases photons. These are produced by positrons or positively charged electrons that annihilate with electrons milliseconds after its emission, releasing two 511-keV photons going in opposite directions. These annihilation photons are detected by the PET scanner scintillation crystals combined to photomultiplier tubes (PMTs), and in many cases an increased number of photons seen on a scan often implies malignancy. However, additional etiologies including, foreign body material, infection and inflammation can also have increased glucose metabolism in the head and neck and skull base and mimic the appearance of skull base neoplasms. This educational exhibit highlights examples of these in the skull base including placement of Teflon material for patulous Eustachian tubes, or vocal cord palsy, infection of the skull base with petrous apicitis from necrotizing otitis externa, and placement of foreign body material for cosmetic injections, with a review of the key pearls and pitfalls involved in PET-CT imaging.

Publication History

Article published online:
07 February 2025